Pretreatment of Plastic Waste: Removal of Colorants from HDPE Using Biosolvents

Abstract

Plastics recycling remains a challenge due to the relatively low quality of the recycled material, since most of the developed recycling processes cannot deal with the additives present in the plastic matrix, so the recycled products end up in lower-grade applications. The application of volatile organic solvents for additives removal is the preferred choice. In this study, pretreatment of plastic packaging waste to remove additives using biosolvents was investigated. The plastic waste used was high-density polyethylene (HDPE) with blue and orange colorants (pigment and/or dye). The first step was to identify the type of colorants present in the HDPE, and we found that both plastics presented only one colorant that was actually a pigment. Then, limonene, a renewable solvent, was used to solubilize HDPE. After HDPE dissolution, a wide range of alcohols (mono-, di-, and tri-alcohols) was evaluated as antisolvents in order to selectively precipitate the polymer and maximize its purity. The use of limonene as solvent for plastic dissolution, in combination with poly-alcohols with an intermediate alkyl chain length and a large number of hydroxyl (OH) groups, was found to work best as an antisolvent (1,2,3-propanetriol and 1,2,4-butanetriol), leading to a removal of up to 94% and 100% of the blue and orange pigments, respectively. Finally, three cycles of extraction were carried out, proving the capability of the solvent and antisolvent to be recovered and reused, ensuring the economic viability and sustainability of the process. This pretreatment provides a secondary source of raw materials and revenue for the recycling process, which may lead to an increase in the quality of recycled polymers, contributing to the development of an economical and sustainable recycling process.

Technical, Economic, and Environmental Comparison of Closed-Loop Recycling Technologies for Common Plastics

“…Dissolution generates quality recyclate at high yields and reasonable prices but has high environmental impacts due to organic solvent use. Switching to biobased solvents such as limonene could minimize fossil resource consumption, but analyses must be conducted on their economic and environmental effects . Switchable solvents, which have reversibly changeable physical properties, offer an opportunity to recycle laminated or multipolymer products. , Ideally, the selected solvent should dissolve the polymer at low temperatures to minimize heat requirements and have a low boiling point to enable energy-efficient recovery by distillation as well as sufficient removal during drying to produce food-grade quality polymer.…”

Greening the physical recycling of HDPE: dissolution precipitation with natural solvents

“…Although it has already been reported that HDPE is soluble in toluene, [27][28][29][32][33][34] xylene, 33,34,57,58 and D-limonene 39 at 110 °C, no dissolution is predicted by the COSMO-SAC model. At this temperature, the experimental solubility limit has only been reported in toluene being between 14.56 wt% 28,35 and 23.1 wt%.…”

“…31 HDPE, the focus of the present study, was the subject of various physical recycling studies using dissolution and precipitation, mostly using toluene, 27,29,[32][33][34][35] xylene 26,33,34 or petroleum ether-based solvents. [36][37][38] Only in 2022, Ferreira et al 39 proposed the use of D-limonene, a biobased solvent, for the dissolution of HDPE. However, the objective of that work was the recovery of dyes from the plastic, and plastic recovery itself was not considered in detail.…”

Assembly strategies for polyethylene-degrading microbial consortia based on the combination of omics tools and the “Plastisphere”

“…In addition, it is uncertain whether the various additives have negative impacts on the process of microbial biodegradation due to their levels of toxicity. Therefore, it is recommended that further studies eliminate additives and other contaminants using pretreatment processes, such as extraction, prior to investigating biodegradation ( Ferreira et al, 2022 ). Alternatively, the integration of strains with specific degradation additives into synthetic consortia could be effective in both degrading the various additives and resolving PE polymers in synergy with other functional bacteria in the consortia.…”